Last weekend I walked along a creek, through the undergrowth and up a scrubby rise for one of those great Litchfield swims.

It's such a precious part of living in the Top End, swimming at the top of a waterfall overlooking the escarpment, with no one else there.

Except, of course, for a water monitor.

And this was a water monitor on a mission. Only a juvenile, it probably measured about 80 centimetres but it was still wrestling a yabby three times the size of its head.

I abandoned the swim and watched this battle, water monitor versus yabby, for almost an hour. First the water monitor had the yabby by the pincers, then slowly, after a bit of tussle, gulp by gulp, the yabby began to descend down its throat.

By the time I left, it was pretty much all over for the yabby.

These are the sights you see on a day trip out of Darwin. I'd been witness to something quite spectacular, and with the water monitor reluctant to relinquish its prey, I was able to take endless close up photos of the whole battle.

But these are the times when you wish you had David Attenborough narrating the experience for you, a husky statesman in the sky explaining the natural world.

So I tracked down Tony Griffiths, a water monitor and goanna expert with the CSIRO and showed him these photos.

Tony examined my pictures. "What I can see is a juvenile water monitor being pretty ambitious and taking a fair bit on. He won't have to worry about having dinner for the next few days, so it's worth his while tackling such a big prey."

Tony also pointed out that the water monitor's rib cage is showing. I asked whether this might be a result of a tougher season in the wild.

Says Tony, "you could hazard a guess that the poorer wet season might have contributed to harder conditions, but it's a young animal so maybe it's still learning to fend for itself. They can also have issues with parasites in the guts as well".

It seemed amazing to me that a water monitor could down a yabby three times the size of its head, but Tony says it's not uncommon.

"You can see from the photos that they've got a very big, elastic mouth, the skin is quite flexible and he can get it down."

Just another day in Litchfield National Park, at the top of a waterfall, overlooking the escarpment.